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post #1 of 3 (permalink) Old 08-15-12, 12:18 PM Thread Starter
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99 Taurus SHO Overdrive issue

Been driving this one since it was 1 year old and still has relatively low mileage - approx. 77K. Just recently started having a problem with regard to the overdrive function. I can be driving along and suddenly the Overdrive Off light comes on, the speedometer behaves erratically, and the RPMs seem, not 100% sure on this, run high. The only way to "reset" the situation is to stop the car and turn off the ignition. Once I turn it back on, and it can be immediately, it is normal, for a bit. My regular drive to work is about 7 miles each way, and it seems to handle that okay. Today I had to go to a meeting out of town and after, approx., 15 to 20 miles, it started acting up again. So, I'm guessing, its possible it might be something temperature related. Unfortunately, definitely thinking transmission (hope not). I did check the tranny fluid (about the extent of my automotive expertise), and it was at the appropriate level and looked clean. Any thoughts will be appreciated (before I end up at my dealers' service dept).
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post #2 of 3 (permalink) Old 08-15-12, 07:04 PM
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Re: 99 Taurus SHO Overdrive issue

Check vacuum line, plugs, and seals and see if there's ant diagnostics. AutoZone or Advanced Auto can probably loan you a scan tool.
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post #3 of 3 (permalink) Old 08-20-12, 10:15 AM
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Re: 99 Taurus SHO Overdrive issue

If the transmission light is on, codes will be stored for up to 50 restarts.

I believe there is an OD solenoid within the transmission that might be faulty. It might also be a couple other things. A bad IAC (idle air controller) can cause havoc on the transmission, along with a throttle position sensor. A bad TPS is often misdiagnosed as a major transmission problem. The IAC can be cleaned. The TPS cannot.

The other problem might be with the A/F ratio. The MAF sensor will get dirty eventually and start throwing the PCM incorrect readings that can result in anything from engine misfire to rpm fluctuations as you mentioned. In most cases the MAF can be cleaned with yes, you guessed it - MAF cleaner, thus saving yourself a couple hundred dollars.

Of course, worst case is that there are multiple problems, or the one problem led to another as more than one sensor has failed. The utmost worst outside of a transmission, is a bad PCM or wiring harness issue that will put the cost in the hundreds of dollars.

Most transmission sensors require dropping the pan, at which time a transmission service is required (about $100 or so). In some cases, a service isn't necessary but if it's been 40K miles since the last service, you're due.

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